A coroner's report says the death was due to "multiple blunt force trauma" consistent with a jump from the parking garage.
"At this point, it is being treated as a suicide until we find evidence otherwise," an Alameda County Coroner's Office spokesman said.
BART police Officer Era Jenkins said investigators are searching for possible witnesses and are looking for video footage from the area.
She said BART detectives are considering all possibilities, including the possibility of a jump, as well as an accidental fall or a push from the parking structure.
"We look for witnesses, we ask for witnesses to come forward -- we just look at all possibilities," Jenkins said, explaining that the coroner's office, not BART police, makes the determination of cause of death.
A BART police lieutenant said someone called police about a body in the bushes around 12:30 p.m. July 19. The body was discovered just feet from the large BART parking structure on the Dublin side.
A LinkedIn profile page lists Joy Grammatica as an implementation manager at Verizon in the San Francisco Bay Area and shows she had been with the company since 2006. Grammatica's father, Calvin Marquis, died on July 17, according to an obituary published in the Pittsburgh Post-Gazette.